Biomedical subjects

Adolfo Martínez-Palomo

Publications and source records attributed to Adolfo Martínez-Palomo.

9 recordsLinked to original sources

PubMed2006

Acanthamoeba castellanii: structural basis of the cytopathic mechanisms.

In this study we report observations on the structural mechanisms of the cytopathic effect of Acanthamoeba castellanii trophozoites on cultured MDCK cell monolayers. Co-incubations were carried out for a maximum of 24h. The first evidence of damage to the cell monolayer was detected by measuring the transepithelial resistance of cell monolayers that interacted with the amoebae. At 6h, transepithelial resistance diminished to 51% and amoebae required 5-6h to produce evidence of structural injury at the light microscopy level. Following 12h of incubation, the cell monolayer was severely damaged. After making intimate contact with the surface of target cells, trophozoites detached cells from the substrate, lysed and by means of food-cups ingested the damaged cells. There was no morphological evidence of modifications in MDCK cell membranes, membrane fusion or junction formation between the amoeba and host plasma membrane. The lytic capacity of the amoebas appears to be the result of cytotoxic factors secreted by the amoebae since, when monolayers were incubated with conditioned medium, there was also a decrease in the transepithelial resistance. Besides, mechanical injury produced by the attachment and movement of the trophozoites may contribute to the disruption of the cell monolayer. As in other pathogenic amoebae, the cytopathic action of A. castellanii on the cell monolayers can subjectively be separated into four stages: adhesion, cytolysis, phagocytosis, and intracellular degradation.

Acanthamoeba↗

PubMed2006

Entamoeba histolytica: ultrastructure of the chromosomes and the mitotic spindle.

We have analyzed by transmission electron microscopy the mitotic process of Entamoeba histolytica trophozoites in an asynchronous population of axenically cultured parasites. Our observations showed that nuclear microtubules, initially located at random in the karyosome during prophase, formed in subsequent stages a mitotic spindle closely related to the nuclear membrane at the polar regions of dividing nuclei. In late prophase and in anaphase, chromosomes appeared as dense bodies 0.1-0.5 microm. At least 15 chromosomes appeared in favorable planes of section, arranged as an incomplete elliptical circle, in close contact with microtubules. There was no morphological evidence of structures resembling the kinetochores of higher eukaryotes. When cut in cross-section, the mitotic spindle was made of 28-35 microtubular rosette assemblies. The latter probably correspond to a similar number of chromosomes, as has been shown by others with pulse-field electrophoresis and fluorescence microscopy of trophozoite spreads. In turn, each microtubular rosette was constituted by 7-12 parallel microtubules. In later stages of the metaphase, two sets of chromosomes were disposed forming a pair of elliptical circles. An additional finding in the dividing nuclei of E. histolytica trophozoites was the presence of compact conglomerates of numerous particles 50 nm in diameter, of similar electron density, shape, and size, probably corresponding to RNA episomes.

Animals↗

PubMed2004

Induction of morphological and electrophysiological changes in hamster cornea after in vitro interaction with trophozoites of Acanthamoeba spp.

Acanthamoeba castellani and Acanthamoeba polyphaga are free-living amebae that cause keratitis and granulomatous encephalitis in humans. We have analyzed the early morphological and electrophysiological changes occurring during the in vitro interaction of cultured amebae with intact or physically damaged corneas obtained from hamsters. Both species of Acanthamoeba produced similar cytopathic changes, as seen by light microscopy and scanning electron microscopy. After adhesion to the epithelial surface, trophozoites formed clumps and migrated toward the cell borders, causing the separation of adjacent cells at 1 h of coculture. At later stages (2 to 4 h), some amebae were found under desquamating epithelial cells whereas others were seen associated with damaged cells or forming amebostome-like structures to ingest detached epithelial cells. Control corneas incubated in culture medium conditioned with amebae showed a cytoplasmic vacuolization and blurring of the epithelial-stromal junction. The early stages of corneal epithelial damage caused by amebae were also analyzed by measuring the transepithelial resistance changes in corneas mounted in Ussing chambers. Both species of Acanthamoeba caused a rapid decrease in electrical resistance. The present observations demonstrate that under in vitro conditions, Acanthamoeba trophozoites rapidly cause significant damage to the corneal epithelium. Furthermore, in our experimental model, previous physical damage to the corneas was not a prerequisite for the development of amebic corneal ulcerations.

Acanthamoeba↗

PubMed2004

Risk of Giardia intestinalis infection in children from an artificially recharged groundwater area in Mexico City.

The objective of this study was to assess the risk of infection with Giardia intestinalis in children living in an area with artificial groundwater recharge and potable water reuse in Mexico City. Eligible wells and surrounding homesteads were defined by using a geographic information system. Five wells were tested for G. intestinalis cysts per 400 liters of water. A total of 750 eligible households were visited during two cross-sectional surveys. Stool samples were provided by 986 children in the rainy season study and 928 children during the dry season survey for parasitologic tests. Their guardians provided information on water, sanitation, hygiene, and socioeconomic variables. The prevalence rates of G. intestinalis infection were 9.4% in the rainy season and 4.4% in the dry season. Higher rates of infection were observed in older individuals (9.5% and 10.6%) and girls had a lower risk of infection than boys (odds ratio [OR] =0.55, 95% confidence interval [CI] = 0.34, 0.88 in the rainy season and OR = 0.47, 95% CI = 0.25, 0.90 in the dry season). During the wet season survey, a health risk was detected among those storing water in unprotected receptacles (OR = 4.00, 4.69, and 5.34 for those using uncovered jars, cisterns or tanks, and buckets, respectively), and bathing outside the dwelling, i.e., using a tap (OR = 1.93, 95% CI = 1.10, 3.39). A health risk was also detected among children from households with unsafe food hygiene practices (OR =2.41, 95% CI =1.10, 5.30) and those with no hand-washing habits (OR = 2.27, 95% CI = 1.00, 5.20). Groundwater reserves are at risk of fecal pollution, as indicated by the presence of G. intestinalis cysts. However, the endemic pattern of intestinal infection reflects low standards of personal hygiene and unsafe drinking water storage and food-related practices at household level. Prevention activities must address health education and environmental protection policies.

Animals↗

PubMed2000

Recent developments in amoebiasis research.

Invasive amoebiasis, the infection of humans by Entamoeba histolytica associated with dysentery and liver abscess, is still a major cause of morbidity and mortality in developing countries. This review attempts to reduce the gap between the overwhelming amount of information coming recently from laboratory research and the sparse contributions resulting from clinical and epidemiological investigations of the second parasitic cause of death resulting from a protozoan parasite.

Journal Article↗

PubMedDate not supplied

Entamoeba histolytica: ultrastructure of trophozoites recovered from experimental liver lesions.

Ultrastructural studies on Entamoeba histolytica have been carried out mostly with trophozoites cultured for many years. Under these conditions, the availability of nutrients and the absence of environmental stimuli may switch off some phenotypic characteristics of the parasite. As a result, virulence of E. histolytica diminishes with prolonged culture passages, and the ability to form cysts disappears in axenically maintained trophozoites. The present analysis by transmission electron microscopy of trophozoites recovered from experimental amebic liver lesions in hamsters revealed two types of cytoplasmic changes. On the one hand, the number of peripheral electron dense granules significantly increased in amebas obtained from liver lesions 15 min and 6h after inoculation. On the other hand, large cytoplasmic vesicles with a microfibrillar content appeared in trophozoites cultured from 72 or 96 h hepatic lesions. With fluorescence microscopy, a chitin-like material was identified in these vesicles by reactivity with calcofluor M2R. Ultrastructurally, these cytoplasmic components resemble the encystation vesicles of Entamoeba invadens and Giardia lamblia. The release of large amounts of electron dense granules, known to contain collagenase activity, probably contributes to degrade extracellular matrix components during tissue invasion. In addition, under the conditions mentioned above, amebas form encystation-like vesicles in an incomplete process of differentiation into cysts, which are the resistant form of the parasite.

Animals↗

PubMedDate not supplied

Trichomonas vaginalis: in vitro attachment and internalization of HIV-1 and HIV-1-infected lymphocytes.

Sexually transmitted diseases (STDs) caused by bacteria and protozoa play an important role in the epidemiology of human immunodeficiency virus (HIV-1) infection. Human trichomoniasis, produced by the protozoan parasite Trichomonas vaginalis, is one of the most common STDs, and is a cause of mucosal lesions in the urogenital tract, which may increase the risk for HIV infection. However, there are no reports concerning the outcome of in vitro interactions between HIV particles and trichomonads. Therefore, we incubated T. vaginalis with three subtypes of HIV-1 (A, B, and D), as well as with HIV-1-infected lymphocytes, and analyzed the interactions with immunofluorescence microscopy and transmission electron microscopy. Our results demonstrated that HIV-1 particles attach and are incorporated into T. vaginalis through endocytic vesicles and are degraded within cytoplasmic vacuoles in approximately 48 h. There was no ultrastructural evidence of HIV-1 replication in trichomonads. These results demonstrated that trichomonads may internalize and harbor HIV-1 particles for short periods of time. In addition, under in vitro conditions, T. vaginalis ingests and digests HIV-1-infected lymphocytes.

Animals↗

PubMedDate not supplied

The ultrastructure of the cyst wall of Giardia lamblia.

Giardiasis is the most common human protozoal infection. In their cystic phase, giardias are protected from the environment by a filamentous cyst wall made up of carbohydrates, proteins, and by two outer membranes separated from the plasma membrane of the parasite by a peripheral space. The present transmission electron microscope observations of G. lamblia cysts of human origin suggest that the extracellular peritrophic space originates from the growth, elongation, and fusion of large cytoplasmic vacuoles. As the large clear vacuoles grew in size, flattening against the inner face of the plasma membrane, they formed a single vacuole that surrounded the body of the parasite, eventually forming two outer membranes. In mature Giardia cysts, the original plasma membrane of the trophozoite becomes the outermost membrane of the cyst wall (CM1). The large vacuoles form a second membrane surrounding the cyst (CM2), and also form a third membrane (CM3), that becomes the new plasma membrane of the trophozoite. During excystation CM1 and CM2 attach to each other and fragment, leaving abundant membrane residues in the peritrophic space. Knowledge of the biochemical composition and functional properties of the complex outer membranous system of G. lamblia cysts here described will be of use to understand the survival of Giardia cysts in the environment, a major factor responsible for the high prevalence of giardiasis worldwide.

Animals↗

PubMedDate not supplied

Ultrastructural study of encystation and excystation in Acanthamoeba castellanii.

Encystation and excystation of Acanthamoeba castellanii were studied by transmission electron microscopy. The differentiation process was induced in asynchronous cultures grown axenically. Cytoplasmic vesicles containing a dense fibrous material very similar in appearance to the cyst wall were observed in trophozoites induced to encyst. When these trophozoites were incubated with calcofluor white m2r, fluorescence was observed in cytoplasmic vesicles, suggesting that the material contained in these vesicles corresponded to cyst wall precursors. Semithin cryosections of mature cysts with the same treatment showed fluorescence in the ectocyst and a less intense fluorescence in the endocyst, suggesting the presence of cellulose in both structures of the cyst wall. In mature cysts induced to excystation, small structures very similar to electron-dense granules (EDG) previously described in other amoebae were frequently observed. The EDGs were either sparsely distributed in the cytoplasm or associated with the cytoplasmic face of the plasma membrane. Many of them were located near the ostiole. In advanced phases of excystation, endocytic activity was suggested by the formation of endocytic structures and the presence of vacuoles with fibrous content similar to that of the cyst wall. Electron-dense granules in the process of dissolution were also observed in these vacuoles. Furthermore, the formation of a pseudopod suggests a displacement of the amoeba toward the ostiole.

Acanthamoeba castellanii↗